NEW DELHI (Reuters) - Sonia Gandhi, president of the ruling Congress party who is widely seen as the country's most powerful politician, was back home from hospital on Tuesday after she took ill during a marathon parliament debate, officials said.

Gandhi, 66, was led limping out of the Lok Sabha on Monday evening by her son and colleagues, and then taken by car to the All India Institute of Medical Sciences hospital in New Delhi.

A Congress party official said Gandhi had a touch of viral fever and was fine now. "Madam Gandhi is home now. She is perfectly fine," the official said.

The Italian-born politician, who has led her party to two successive terms governing the world's largest democracy, has played a slightly reduced public role since being treated abroad for an unknown illness in 2011. Still, she is the world's sixth most powerful woman, Forbes magazine said last year.

The party is usually very secretive about Gandhi's health, but several media reports said in 2011 that she had been treated for cancer at New York's Sloan-Kettering Cancer Center.

On Monday, Gandhi participated in a parliament debate on a scheme to provide cheap food to more than two-thirds of India's poor - one of her pet projects - when she felt unwell.

Gandhi and her son, Rahul, are banking on the nearly $20-billion food security programme to boost the Congress party's prospects ahead of a difficult election next year and the party's campaign is built around the two members of the Nehru-Gandhi dynasty.

FOOD FOR ALL PROGRAMME

Television images showed the normally strong-looking leader trembling as she read out from a clutch of papers a short speech on the food security bill, one of the world's largest welfare programmes and one that Gandhi has insisted on to ensure India's poor are not left behind in its emergence as an economic power.

"It's time to take the historic step," she said. "It is my fervent appeal that we shall pass this unanimously."

Critics say the programme will strain government finances further at a time when the economy has slowed and the country's external imbalance has deteriorated, with the rupee currency languishing at record lows.

The food security bill was passed two hours after Gandhi and her son left parliament. It must now go to the Rajya Sabha.

Gandhi became Congress party president some years after the 1991 assassination of her husband, former Indian prime minister Rajiv Gandhi.

She declined to become prime minister despite pressure from the party after the first victory in 2004, and chose the quiet economist Manmohan Singh for the top job. However, she arguably wields more power over policy than the prime minister.

Her son is now leading the party's preparations for a national election - due to be held in less than a year.

The Gandhi family, descended from India's first prime minister, Jawaharlal Nehru, enjoys a status similar to royalty in the country of 1.2 billion. They are not related to independence hero Mahatma Gandhi, a close ally of Nehru. (Editing by John Chalmers and Clarence Fernandez)